Systems and methods for posterior dynamic stabilization of the spine

ABSTRACT

Devices, systems and methods for dynamically stabilizing the spine are provided. The devices include an expandable spacer or member having an unexpanded configuration and an expanded configuration, wherein the expandable member in an expanded configuration has a size, volume and/or shape configured for positioning between the spinous processes of adjacent vertebrae in order to distract the vertebrae relative to each other. The systems include one or more expandable members and a mechanical actuation means for expanding the expandable member. The methods involve the implantation of one or more devices or expandable spacers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/658,756, now U.S. Pat. No. 9,314,279, filed on Oct. 23, 2012, whichis a continuation of U.S. patent application Ser. No. 11/052,002, nowU.S. Pat. No. 8,317,684, filed on Feb. 4, 2005, which is acontinuation-in-part of U.S. patent application Ser. No. 11/006,502, nowU.S. Pat. No. 8,123,807, filed on Dec. 6, 2004, which is acontinuation-in-part of U.S. patent application Ser. No. 10/970,843, nowU.S. Pat. No. 8,167,944, filed on Oct. 20, 2004, all of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention is directed towards the treatment of spinaldisorders and pain. More particularly, the present invention is directedto systems and methods of treating the spine that eliminate pain andenable spinal motion which effectively mimics that of a normallyfunctioning spine.

BACKGROUND

FIG. 1 illustrates a portion of the human spine having a superiorvertebra 2 and an inferior vertebra 4, with an intervertebral disc 6located in between the two vertebral bodies. The superior vertebra 2 hassuperior facet joints 8 a and 8 b, inferior facet joints 10 a and 10 b,and spinous process 18. Pedicles 3 a and 3 b interconnect the respectivesuperior facet joints 8 a, 8 b to the vertebral body 2. Extendinglaterally from superior facet joints 8 a, 8 b are transverse processes 7a and 7 b, respectively. Extending between each inferior facet joints 10a and 10 b and the spinous process 18 are laminal zones 5 a and 5 b,respectively. Similarly, inferior vertebra 4 has superior facet joints12 a and 12 b, superior pedicles 9 a and 9 b, transverse processes 11 aand 11 b, inferior facet joints 14 a and 14 b, laminal zones 15 a and 15b, and spinous process 22.

The superior vertebra with its inferior facets, the inferior vertebrawith its superior facet joints, the intervertebral disc, and sevenspinal ligaments (not shown) extending between the superior and inferiorvertebrae together comprise a spinal motion segment or functional spineunit. Each spinal motion segment enables motion along three orthogonalaxes, both in rotation and in translation. The various spinal motionsare illustrated in FIGS. 2A-2C. In particular, FIG. 2A illustratesflexion and extension motions and axial loading, FIG. 2B illustrateslateral bending motion and FIG. 2C illustrates axial rotational motion.A normally functioning spinal motion segment provides physiologicallimits and stiffness in each rotational and translational direction tocreate a stable and strong column structure to support physiologicalloads.

Traumatic, inflammatory, metabolic, synovial, neoplastic anddegenerative disorders of the spine can produce debilitating pain thatcan affect a spinal motion segment's ability to properly function. Thespecific location or source of spinal pain is most often an affectedintervertebral disc or facet joint. Often, a disorder in one location orspinal component can lead to eventual deterioration or disorder and,ultimately, pain in the other.

Spine fusion (arthrodesis) is a procedure in which two or more adjacentvertebral bodies are fused together. It is one of the most commonapproaches to alleviating various types of spinal pain, particularlypain associated with one or more affected intervertebral discs. Whilespine fusion generally helps to eliminate certain types of pain, it hasbeen shown to decrease function by limiting the range of motion forpatients in flexion, extension, rotation and lateral bending.Furthermore, the fusion creates increased stresses on adjacent non-fusedmotion segments and accelerated degeneration of the motion segments.Additionally, pseudarthrosis (resulting from an incomplete orineffective fusion) may not provide the expected painrelief for thepatient. Also, the device(s) used for fusion, whether artificial orbiological, may migrate out of the fusion site, creating significant newproblems for the patient.

Various technologies and approaches have been developed to treat spinalpain without fusion in order to maintain or re-create the naturalbiomechanics of the spine. To this end, significant efforts are beingmade in the use of implantable artificial intervertebral discs.Artificial discs are intended to restore articulation between vertebralbodies so as to re-create the full range of motion normally allowed bythe elastic properties of the natural disc. Unfortunately, the currentlyavailable artificial discs do not adequately address all of themechanics of motion for the spinal column.

It has been found that the facet joints can also be a significant sourceof spinal disorders and debilitating pain. For example, a patient maysuffer from arthritic facet joints, severe facet joint tropism,otherwise deformed facet joints, facet joint injuries, etc. Thesedisorders lead to spinal stenosis, degenerative spondylolisthesis,and/or isthmic spondylolisthesis, pinching the nerves that extendbetween the affected vertebrae.

Current interventions for the treatment of facet joint disorders havenot been found to provide completely successful results. Facetectomy(removal of the facet joints) may provide some pain relief; but as thefacet joints help to support axial, torsional, and shear loads that acton the spinal column in addition to providing a sliding articulation andmechanism for load transmission, their removal inhibits natural spinalfunction. Laminectomy (removal of the lamina, including the spinal archand the spinous process) may also provide pain relief associated withfacet joint disorders; however, the spine is made less stable andsubject to hypermobility. Problems with the facet joints can alsocomplicate treatments associated with other portions of the spine. Infact, contraindications for disc replacement include arthritic facetjoints, absent facet joints, severe facet joint tropism, or otherwisedeformed facet joints due to the inability of the artificial disc (whenused with compromised or missing facet joints) to properly restore thenatural biomechanics of the spinal motion segment.

While various attempts have been made at facet joint replacement, theyhave been inadequate. This is due to the fact that prosthetic facetjoints preserve existing bony structures and therefore do not addresspathologies that affect facet joints themselves. Certain facet jointprostheses, such as those disclosed in U.S. Pat. No. 6,132,464, areintended to be supported on the lamina or the posterior arch. As thelamina is a very complex and highly variable anatomical structure, it isvery difficult to design a prosthesis that provides reproduciblepositioning against the lamina to correctly locate the prosthetic facetjoints. In addition, when facet joint replacement involves completeremoval and replacement of the natural facet joint, as disclosed in U.S.Pat. No. 6,579,319, the prosthesis is unlikely to endure the loads andcycling experienced by the vertebra. Thus, the facet joint replacementmay be subject to long-term displacement. Furthermore, when facet jointdisorders are accompanied by disease or trauma to other structures of avertebra (such as the lamina, spinous process, and/or transverse processfacet joint replacement is insufficient to treat the problem(s)).

Most recently, surgical-based technologies, referred to as “dynamicposterior stabilization,” have been developed to address spinal painresulting from more than one disorder, when more than one structure ofthe spine has been compromised. An objective of such technologies is toprovide the support of fusion-based implants while maximizing thenatural biomechanics of the spine. Dynamic posterior stabilizationsystems typically fall into one of two general categories: posteriorpedicle screw-based systems and interspinous spacers.

Examples of pedicle screw-based systems are disclosed in U.S. Pat. Nos.5,015,247, 5,484,437, 5,489,308, 5,609,636 and 5,658,337, 5,741,253,6,080,155, 6,096,038, 6,264,656 and 6,270,498. These types of systemsinvolve the use of screws that are positioned in the vertebral bodythrough the pedicle. Certain types of these pedicle screw-based systemsmay be used to augment compromised facet joints, while others requireremoval of the spinous process and/or the facet joints for implantation.One such system, the Zimmer Spine Dynesys® employs a cord which isextended between the pedicle screws and a fairly rigid spacer which ispassed over the cord and positioned between the screws. While thissystem is able to provide load sharing and restoration of disc height,because it is so rigid, it is not effective in preserving the naturalmotion of the spinal segment into which it is implanted. Other pediclescrew-based systems employ articulating joints between the pediclescrews. Because these types of systems require the use of pediclescrews, the systems are often more invasive to implant than interspinousspacers.

Where the level of disability or pain to the affected spinal motionsegments is not that severe or where the condition, such as an injury,is not chronic, the use of interspinous spacers is preferred overpedicle screw-based systems as spacers require a less invasiveimplantation approach and less dissection of the surrounding tissue andligaments. Examples of interspinous spacers are disclosed in U.S. Pat.No. RE36,211, U.S. Pat. Nos. 5,645,599, 6,149,642, 6,500,178, 6,695,842,6,716,245 and 6,761,720. The spacers, which are made of either a hard orcompliant material, are placed in between adjacent spinous processes.The harder material spacers are fixed in place by means of the opposingforce caused by distracting the affected spinal segment and/or by use ofkeels or screws that anchor into the spinous process. While slightlyless invasive than the procedures required for implanting a pediclescrew-based dynamic stabilization system, implantation of hard or solidinterspinous spacers still requires dissection of muscle tissue and ofthe supraspinous and interspinous ligaments. Additionally, these tend tofacilitate spinal motion that is less analogous to the natural spinalmotion than do the more compliant and flexible interspinous spacers.Another advantage of the compliant/flexible interspinous spacers is theability to deliver them somewhat less invasively than those that are notcompliant or flexible; however, their compliancy makes them moresusceptible to displacement or migration over time. To obviate thisrisk, many of these spacers employ straps or the like that are wrappedaround the spinous processes of the vertebrae above and below the levelwhere the spacer is implanted. Of course, this requires some additionaltissue and ligament dissection superior and inferior to the implantsite, i.e., at least within the adjacent interspinous spaces.

With the limitations of current spine stabilization technologies, thereis clearly a need for an improved means and method for dynamic posteriorstabilization of the spine that address the drawbacks of prior devices.In particular, it would be highly beneficial to have a dynamicstabilization system that involves a minimally invasive implantationprocedure, where the extent of distraction between the affectedvertebrae is adjustable upon implantation and at a later time ifnecessary. It would be additionally advantageous if the system or devicewas also removable in a minimally invasive manner.

SUMMARY

The present invention provides devices, systems and methods forstabilizing at least one spinal motion segment. The devices include anexpandable spacer or member having an unexpanded configuration and anexpanded configuration, wherein the expandable member in an expandedconfiguration has a size, volume and/or shape configured for positioningbetween the spinous processes of adjacent vertebrae in order to distractthe vertebrae relative to each other.

In certain embodiments, the expandable member is a balloon made ofeither non-compliant or compliant material which may be porous ornon-porous, or may include a mesh material which may be coated or linedwith a porous or non-porous material. The device may further include aport for coupling to a source of an inflation and/or expansion mediumfor inflating and/or expanding the expandable member. In certainembodiments, the port may be used to deflate or evacuate the expandablemember. The devices may further include one or more tabs for anchoringthe expandable member to the spinous processes. Optionally, the devicemay include one marker on a surface of the expandable member tofacilitate fluoroscopic imaging.

In other embodiments, the expandable members are cages, struts, wires orsolid objects having annular, spherical or elliptical shapes when in anexpanded condition. The expandable members may be self-expanding oradjustably expandable depending on the extent of distraction required.

The invention further includes systems for stabilizing at least onespinal motion segment which include one or more expandable members andan expansion medium for injection within or for filling the interior ofthe expandable member via the port. The subject systems may furtherinclude at least one means for anchoring or securing the expandablemember to the spinal motion segment.

The invention further includes methods for stabilizing at least onespinal motion segment which involve the implantation of one or moredevices or expandable spacers of the present invention, in which theexpandable member is positioned between the spinous processes ofadjacent vertebrae in an unexpanded condition and then subsequentlyexpanded to a size and/or shape for selectively distracting the adjacentvertebrae. The invention also contemplates the temporary implantation ofthe subject devices which may be subsequently removed from the patientonce the intended treatment is complete. Many of the methods involve thepercutaneous implantation of the subject devices.

These and other objects, advantages, and features of the invention willbecome apparent to those persons skilled in the art upon reading thedetails of the invention as more fully described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in conjunction with the accompanying drawings. It isemphasized that, according to common practice, the various features ofthe drawings are not to-scale. On the contrary, the dimensions of thevarious features are arbitrarily expanded or reduced for clarity.Included in the drawings are the following figures:

FIG. 1 illustrates a perspective view of a portion of the human spinehaving two vertebral segments.

FIGS. 2A-2C illustrate left side, dorsal and top views, respectively, ofthe spinal segments of FIG. 1A undergoing various motions.

FIG. 3A illustrates an interspinous device of the present invention inan unexpanded or collapsed state coupled to a cannula of the deliverysystem of the present invention. FIG. 3B is an enlarged view of theinterspinous device of FIG. 3A.

FIG. 4A illustrates an interspinous device of the present invention inan expanded state coupled to a cannula of the delivery system of thepresent invention. FIG. 4B is an enlarged view of the interspinousdevice of FIG. 4A.

FIGS. 5A-5C illustrates top, dorsal and side views of an initial step ofthe method of the present invention in which a cannula is delivered tothe target implant site.

FIGS. 6A and 6B illustrate dorsal and side views of the step ofdissecting an opening within the spinous ligament utilizing a cuttinginstrument of the system of FIGS. 3 and 4. FIG. 6C is an enlarged viewof the target area within the spinous ligament.

FIGS. 7A and 7B illustrate dorsal and side views of the step ofinserting the interspinous device of FIG. 4A into the dissected openingof the spinous ligament. FIGS. 7C and 7D are enlarged views of thetarget area in FIGS. 7A and 7B, respectively.

FIGS. 8A and 8B illustrate dorsal aid and side views of the step ofinflating or expanding the interspinous device of FIG. 4A within theimplant site. FIGS. 8C and 8D are enlarged views of the target area inFIGS. 8A and 8B, respectively.

FIG. 9A illustrates a side view of the step of filling the interspinousdevice of FIG. 4A with an expansion medium. FIG. 9B is an enlarged viewof the target area in FIG. 9A.

FIG. 10A illustrates a dorsal view of the step of further securing theinterspinous device of FIG. 4A within the implant site. FIG. 10B is anenlarged view of the target area in FIG. 10A.

FIGS. 11A and 11B illustrate dorsal and side views of the step ofinserting another embodiment of an interspinous device into thedissected opening of the spinous ligament. FIGS. 11C and 11D areenlarged views of the target area in FIGS. 11A and 11B, respectively.

FIGS. 12A and 12B illustrate dorsal and side views of the step ofexpanding the interspinous device of FIGS. 11A-11D within the implantsite. FIGS. 12C and 12D are enlarged views of the target area in FIGS.12A and 12B, respectively.

FIG. 13A illustrates a side view of the step of filling the interspinousdevice of FIGS. 11A-11D with an expansion medium. FIG. 13B is anenlarged view of the target area in FIG. 13A.

FIGS. 14A-14F illustrate dorsal views of another interspinous device ofthe present invention and a device for implanting the interspinousdevice where the implantation device is used initially to distract theinterspinous space prior to implanting the interspinous device.

FIGS. 15A and 15B illustrate dorsal views of another interspinous deviceof the present invention implanted within an interspinous space.

FIGS. 16A and 16B illustrate dorsal views of another interspinous deviceof the present invention implanted within an interspinous space. FIG.16C is a side view of FIG. 16B.

FIGS. 17A and 17B illustrate side views of another interspinous deviceof the present invention implanted within an interspinous space. FIG.17C is a dorsal view of FIG. 17B.

FIGS. 18A and 18B illustrate another interspinous device of the presentinvention in undeployed and deployed states, respectively.

FIGS. 19A and 19B illustrate the device of FIG. 18 implanted within aninterspinous space and operably coupled to a delivery device of thepresent invention.

FIGS. 20A and 20B illustrate cut-away views of two embodiments of thehandle portion of the delivery device of FIGS. 19A and 19B.

FIG. 21 illustrates a cut-away view of a distal portion of the device ofFIG. 18 operably positioned over the delivery device of FIG. 20B.

DETAILED DESCRIPTION

Before the subject devices, systems and methods are described, it is tobe understood that this invention is not limited to particularembodiments described, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present invention will be limited onlyby the appended claims.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “aspinal segment” may include a plurality of such spinal segments andreference to “the screw” includes reference to one or more screws andequivalents thereof known to those skilled in the art, and so forth.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassedwithin the invention. The upper and lower limits of these smaller rangesmay independently be included or excluded in the range, and each rangewhere either, neither or both limits are included in the smaller rangesis also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included in the invention.

All publications mentioned herein are incorporated herein by referenceto disclose and describe the methods and/or materials in connection withwhich the publications are cited. The publications discussed herein areprovided solely for their disclosure prior to the filing date of thepresent application. Nothing herein is to be construed as an admissionthat the present invention is not entitled to antedate such publicationby virtue of prior invention. Further, the dates of publication providedmay be different from the actual publication dates which may need to beindependently confirmed.

The present invention will now be described in greater detail by way ofthe following description of exemplary embodiments and variations of thedevices and methods of the present invention. The invention generallyincludes an interspinous spacer device as well as instruments for thepercutaneous implantation of the interspinous spacer. A key feature ofthe interspinous spacer device is that it is expandable from a lowprofile configuration to a higher profile or operative configuration.This design allows the device, when in the low profile condition, to bedelivered by percutaneous means without requiring the removal of anyportion of the spinal motion segment into which the device is implanted.

Referring now to the drawings and to FIGS. 3 and 4 in particular, anexemplary interspinous spacer device 24 of the present invention isillustrated in collapsed and expanded configurations, respectively.Interspinous device 24 includes an expandable spacer body 34 that has asize and shape when in the expanded condition for operative positioningbetween the spinous processes of adjacent superior and inferiorvertebrae of the spinal motion segment being treated. Expandable body 34is made of an expandable or inflatable biocompatible material such asnon-porous material, e.g., latex, acrylate or a metal mesh, e.g., anitinol or titanium cage.

Those spacers made of an inflatable non-porous material, i.e., balloontype spacers (see FIGS. 3-10), are inflated with an inflation orexpansion medium, such as air, saline, another biologically compatiblefluid, or a flowable solid material, such as polyurethane, or a gel,which thickens or hardens substantially upon injection into balloon 34.In one embodiment, balloon 34 is initially inflated with air to providesome structure or rigidity to it to facilitate its optimum positioningand alignment between the spinous processes. Once positioned as desired,balloon 34 is injected with a flowable solid material (the air thereinbeing displaced possibly via a vent hole within port 32). In certainembodiments, the expandable body is made of a non-compliant orsemi-compliant material so as to maintain a substantially fixed shape orconfiguration and ensure proper, long-term retention within the implantsite. In other embodiments, the expandable member may be made of acompliant material. In any embodiment, the compressibility andflexibility of balloon 34 can be selected to address the indicationsbeing treated.

Other embodiments of the subject spacers are made of an expandable meshor cage (see FIGS. 11-12). The mesh or cage may be made of asuper-elastic memory material which is compressible for delivery througha cannula and which is self-expanding upon implantation. Upon expansion,the mesh or cage may be self-retaining whereby its struts, links orwires are sufficiently rigid by themselves to maintain the expandedcondition and withstand the natural forces exerted on it by the spine.The mesh or cage may have an exterior coating or an interior lining madeof materials similar to or the same as that used for the balloonspacers, or may otherwise be embedded in such material. In certainembodiments, an expansion medium may be used to fill the interior of thecage or mesh structure, such as with a biologically compatible fluid orflowable solid material used with the balloon-type embodiments.

In certain embodiments of present invention, either during the implantprocedure or in a subsequent procedure, the size or volume of theimplanted expandable spacer may be selectively adjusted or varied. Forexample, after an initial assessment upon implant, it may be necessaryto adjust, either reduce or increase, the size or volume of the spacerto optimize the intended treatment. Further, it may be intended to onlytemporarily implant the spacer for the purpose of treating a temporarycondition, e.g., an injured or bulging or herniated disk. Once therepair is achieved or the treatment completed, the spacer may beremoved, either with or without substantially reducing the size orvolume of the spacer. In other embodiments, the spacer as well as theinflation/expansion material may be made of biodegradable materialswherein the spacer degrades after a time in which the injury is healedor the treatment completed.

When unexpanded or deflated, as shown in FIGS. 3A and 3B (balloon type)and in FIGS. 11C and 11D (mesh type), expandable body 34 has a lowprofile, such as a narrow, elongated shape, to be easily translatedthrough a delivery cannula 70. The shape of expandable body 34, when inan expanded or inflated state, has a larger profile which is generallyH-shaped. Expandable body 34 has lateral or side portions 30, endportions 26 and apexes 28 defined between the side portions 30 and theend portions 26. End portions 26 are preferably recessed or contoured toprovide a narrowed central portion along the height dimension or majoraxis of expandable body 34 to readily fit between and to conform to thespinous processes. Accordingly, expandable body 34 has an apex-to-apexdimension (i.e., height or major axis dimension) from about 3 to about 5cm and a width dimension (minor axis dimension) from about 2 to about 4cm.

For those embodiments of expandable bodies which comprise a balloonconfiguration, balloon 34 has an inflation or injection port 32 at asidewall 30 for coupling to a source of inflation or expansion materialor medium. Port 32 may consist of a one-way valve which is self-sealingupon release from an inflation mechanism or tube 76. Port 32 is furtherconfigured to releasably engage from tube 76, where such engagement maybe threaded or involve a releasable locking mechanism. Where theexpandable body comprises a mesh or cage, port 32 simply acts as an exitport, however, where an expansion material is used, it also functions asan injection port for the expansion material.

Optionally, device 24 may include a pair of tabs 36 which may bepositioned on one side of the device where the tabs 36 are preferablysituated at the apexes 28 of expandable body 34. Pins or screws (not yetshown) may be used to secure the tabs against the spinous process tofurther ensure long-term retention of device 24 within the implant site.Tabs 36 are made of a biocompatible material, such as latex, acrylate,rubber, or a metal, and may be made of the same material used for theexpandable member 34. Shown here attached to tabs 36 are tethers 38which are used in part to manipulate the positioning of expandable body34 upon implantation into the targeted spinal motion segment. Thetethers may be made of any suitable material including but not limitedto materials used to make conventional sutures. They may also be made ofa biodegradable material. While two tabs and associated tethers areprovided in the illustrated embodiment, one, three or more may beemployed, where the respective tabs are located on the expandable bodyso as to be adjacent a bony structure of the vertebra suitable foranchoring thereto. In embodiments which do not employ securing tabs 36,tethers 38 may be attached directly to the expandable body itself.

Optionally still, device 24 may further include radiopaque markers 40 onthe surface of expandable body 34 visible under fluoroscopic imaging tofacilitate positioning of the expandable body. Any number of markers 40may be employed anywhere on expandable body 34, however, as few as fourmarkers, one at each apex, may be sufficient. With embodiments employingcage or mesh expandable bodies, the cage or mesh material itself may beradiopaque.

A system of the present invention includes a cannula device 70 having anouter sheath 72, a proximal hub 78 and preferably at least two interiorlumens 74, 76 for the percutaneous delivery of the device and othertools for implanting the device, which tools may include a cuttinginstrument 60 (see FIG. 6C), a device delivery instrument 77, anendoscope, etc., which tools will be further discussed in the context ofthe description of the subject methods with reference to FIGS. 5-10.

In FIGS. 5A-5C, the spinal motion segment of FIG. 1 is illustratedhaving spinal ligament 54 extending between the superior spinous process18 and the inferior spinous process 22. A percutaneous puncture is madeinto the skin 30 adjacent the target spinal motion segment of a patientundergoing the implantation of the interspinous device of the presentinvention, and a cannula 70 is penetrated to the spinous ligament 54.The puncture and subsequent penetration may be made by way of a sharpdistal tip of cannula 70 or by a trocar (not shown) delivered through alumen of cannula 70.

As illustrated in FIGS. 6A-6C, the spinous ligament 54 is then dissectedand an opening 58 created therein by way of a cutting instrument 60,such as a simple scalpel, an electrosurgical device or the like,delivered through a lumen of cannula 70. Cutting instrument 60 may thenbe removed from cannula 70 and, as illustrated in FIGS. 7A-7D (balloontype) and in FIGS. 11A-11D (cage type), a delivery instrument 16 havinginterspinous device 24 operatively preloaded is delivered throughcannula 70.

The preloading of device 24 to delivery instrument 76 involves providingexpandable body 34 in an unexpanded or deflated state and releasablycoupled, as described above, by way of inflation or injection port 32 ofexpandable body 34 to the distal end of delivery instrument 76. Inaddition to functioning as a pusher, instrument 76 may act as aninflation lumen for balloon type embodiments through which an inflationmedium is transported to within expandable body 34.

Depending upon the material used to fabricate expandable body 34, theexpandable body may have a degree of stiffness in an unexpanded ordeflated state such that it may maintain an elongated configuration soas to be directly insertable and pushable through cannula 70. This maybe the case where the expandable member 34 is made of a cage or meshmaterial. Alternatively, a pusher or small diameter rod (not shown) maybe inserted through inflation port 32 to within expandable body 34 tokeep it in an elongated state so as to prevent expandable body 34 frombunching within cannula 70 and to provide some rigidity to moreeffectively position the expandable body in the target implant site. Therod is then removed from expandable body 34 and from delivery device 76upon positioning the expandable body at the target implant site. Ineither case, expandable body 34 is folded or compressed about its minoraxis with the side wall opposite the inflation port 32 defining a distalend 25 (see FIG. 3B) and the apexes 28 of the expandable body foldedproximally of distal end 25 to provide a streamlined, low profileconfiguration for delivery through cannula 70.

Once interspinous device 24 is preloaded to delivery device 76 as justdescribed, device 24 is then inserted into a lumen of cannula 70 withtethers 38 pulled back and trail proximally so that the tether ends 38 aextend from hub 78 of cannula 70. Expandable body member 34 istranslated through cannula 70 to within opening 58 within spinousligament 54 as best illustrated in FIGS. 7C and 11C. For best results,expandable body 34 is centrally positioned within opening 58 so that thecountered ends 26 of expandable body 34 readily engage with the opposedspinous processes 18, 22. Fluoroscopy may be employed to visualizemarkers 40 so as to ensure that expandable body 34 centrally straddlesthe spinous ligament opening 58, i.e., the markers on the distal side 25of the expandable body are positioned on one side of the spine and themarkers on the proximal side of the expandable body (the side on whichport 32 is located) are positioned on the other side of the spine.

Once centrally positioned, expandable body 34 is inflated or expanded,as illustrated in FIGS. 8A-8D and 12A-12D. For balloon spacers,inflation occurs by allowing an inflation or expansion medium, asdiscussed above, to enter into the interior of the expandable body viaport 32. For expandable mesh spacers, the expandable body may beconfigured to expand automatically upon exiting cannula 70. Theinflation or expansion of expandable body 34 may also be visualizedunder fluoroscopy whereby markers 40, as best shown in FIG. 8C, areobserved and the position of expandable body 34 may be adjusted toensure optimum positioning upon complete inflation. Adjustments of theexpandable body's position may be accomplished by manually pulling onone or both tether ends 38 a which in turn pulls on tabs 36 to which thetethers 38 are attached at their proximal ends. The tethers 38 areselectively pulled as necessary to center or optimally positioninterspinous expandable body 34 to achieve the desired treatment of thetargeted spinal motion segment.

With embodiments in which the expandable body is initially inflated withair and then filled with a solid or fluid medium, the latter ispreferably not delivered or injected into the interior of the expandablebody until the position of the expandable body within the interspinousspace has been verified and optimized. This is beneficial in situationswhere, upon inflation, it is found that the expandable body ismisaligned within the interspinous space and requires repositioning. Theexpandable body may simply be deflated of air to the extent necessaryand repositioned in a less inflated or deflated state. If necessary, forexample where it is found that the maximum spacer or expandable bodysize is insufficient for the particular application at hand, expandablebody 34 may be completely deflated and removed and replaced with a moresuitably sized unit.

For balloon spacers and those mesh spacers which are not by themselvessufficiently self-retaining, once the position and extent of inflationor expansion of expandable body 34 are optimized, the expansion medium,e.g., polyurethane, is allowed to flow or injected into the interior ofthe expandable body via port 32. As illustrated in FIGS. 9A and 9B,expandable body 34 is caused to expand to a selected volume and in sodoing forces apart (see arrow 80) the spinous processes 18, 22 inbetween which it is situated. This selective distraction of the spinousprocesses also results in distraction of the vertebral bodies 2, 4 (seearrow 82) which in turn allows the disk, if bulging or distended, toretract to a more natural position (see arrow 84). Again, the extent ofdistraction or lordosis undergone by the subject vertebrae can bemonitored by observing expandable body markers 40 under fluoroscopy.

The extent of possible distraction may be limited by the capacity ofexpandable body 34 and the type of expandable body material employed. Incertain embodiments, such as expandable bodies made of non-compliant orsemi-compliant balloons, the requisite volume of the inflation mediummay be substantially fixed whereby the balloon achieves its fullyexpanded configuration upon filling it with the fixed volume of medium.In other embodiments, such as with balloons made of a compliantmaterial, the extent of expansion may be variable and selectableintraoperatively depending on the extent of lordosis or distraction tobe achieved between the spinous processes in which balloon 34 is nowinterposed.

Upon achieving the desired distraction between the vertebrae,inflation/expansion lumen 76 is disengaged from expandable body port 32which then becomes sealed by means of a one-way valve that is closedupon disengagement of lumen 76. Inflation/expansion lumen is thenremoved from cannula 70. While the opposing compressive force exerted onexpandable body 34 by the distracted spinous processes 18, 22 may besufficient to permanently retain expandable body 34 therebetween, theinterspinous device may be further secured to the spinous processes 18,22 to ensure that the expandable body does not slip or migrate from itsimplanted position. To this end, tabs 36 are anchored to the spinousprocesses as illustrated in FIGS. 10A and 10B and in FIGS. 13A and 13B.Any type of anchoring means, such as screws, tacks, staples, adhesive,etc. may be employed to anchor tabs 36. Here, cannulated screws 90 areused as anchors and are delivered to the target site releasably coupledto screw driving instrument 88. While various screw attachment andrelease mechanisms may be employed, a simple configuration involvesproviding the screws 90 with a threaded inner lumen which is threadablyengagable with the threaded distal end of instrument 88.

To ensure accurate placement of the screws 90, the screws 90 along withinstrument 88, can be tracked and translated over respective tethers 38,which function as guide wires. By manipulating instrument 88, the screwsare driven or screwed into the respective spinous process. Screwdriver88 is then disengaged or unscrewed from screw 90. After both tabs 36 aresecurely anchored to the spinous processes, the screwdriver and thecannula may be removed from the patient's back.

FIGS. 14A-14F illustrate an alternative method for implanting theexpandable member. In particular, the method contemplates pre-inflatingor pre-expanding the expandable member prior to positioning theexpandable member within the interspinous space. To accomplish this, thevertebrae 2 and 4 may be distracted prior to insertion of thepre-expandable balloon implant. A temporary distraction mechanism, suchas another balloon or a mechanically actuated device, is inserted intothe interspinous space. When the desired amount of distraction isachieved, the permanent or implantable expandable member can then beplaced within the interspinous space, and the temporary distractionmember may then be removed from the space.

While certain of the expandable spacers are intended to be permanentlyimplanted within a spine, certain others may be implanted onlytemporarily to facilitate the healing of an injury or the treatment of areversible or non-chronic condition, such as a herniated disk. For suchtemporary treatments, the expansion material most likely is a fluid,such as saline, which may be easily aspirated through port 32 or may beallowed to drain out via a penetration or cut made in the expandablemember. In those embodiments in which the expansion material is aflowable solid, which may or may not subsequently harden within theexpandable member, the material may be one that is reconstitutable intoa liquid form which may then be subsequently aspirated or evacuated fromthe expandable member. For percutaneous removal of the expandablemember, a cannula such as cannula 70 may be used and an aspirationinstrument delivered therethrough and coupled to port 32. Afterdeflation and/or evacuation of the expandable member, and removal of thetacks, sutures, staples, etc. if such are used to secure tabs 36, theexpandable member may be easily removed through cannula 70. Withbiodegradable spacers, removal of the spacer is obviated.

It should be noted that any of the above-described steps or procedures,including but not limited to cannulation of the target area, dissectionof the spinous ligament, insertion of the expandable body within thedissected opening of the spinous ligament, inflation and/or expansion ofthe expandable body, adjustment or readjustment of the expandable body,and anchoring of the tabs, etc., may be facilitated by way of a scope 62delivered through a lumen of cannula 70 to the open distal tip ofcannula 70. Alternatively, a second cannula delivered through anotherpercutaneous penetration may be employed for use of an endoscope and anyother instruments needed to facilitate the procedure.

FIG. 14A illustrates an exemplary embodiment of a temporary distractionmechanism 100 having an expandable strut configuration. Mechanism 100includes bilateral struts 102 which are hinged and foldable at hubs 104,respectively. Bridging the struts 102 at superior and inferior ends arespinous process engagement portions 106 which are preferably configuredto conformingly engage with the spinous processes 18, 22. Extendingcentrally between hubs 104 is a distal portion of guide wire 108, whichalso extends proximally through proximal hub 104 a. Guide wire 108 is inthreaded engagement with both hub 104 a whereby hub 104 a can betranslated both proximally and distally along guide wire 108. As such,expandable member 100 can be provided in a low-profile, compressed stateupon proximally translating hub 104 a in a proximal direction. In such alow-profile state, distraction mechanism 100 is easily deliverablethrough cannula 70, as described above, to the interspinous space. Uponproper positioning, distraction mechanism 100 is expandable to a higherprofile or expanded state by translating hub 104 a toward hub 104 b in adistal direction along guide wire 108, as illustrated in FIG. 14A.

After the desired amount of distraction is achieved between vertebrae 2and 4, an implantable expandable member 110 of the present invention isdelivered adjacent the distracted spinal motion segment. Expandablemember 110 may be delivered from the same incision and side asdistraction mechanism 100 (ipsolateral approach) and as well as throughthe same working channel, or may be delivered through a differentincision on the same or opposing side of the spinal motion segment beingtreated (bilateral approach) using two different working channels. Inthe illustrated embodiment, expandable member 110 is delivered from thesame side of the spinous process as distraction mechanism 100.Expandable member 110 may be delivered through a separate designatedlumen in cannula 70 and translated distally of hub 104 b of distractionmechanism 100.

As shown in FIG. 14B, after deployment, expandable member 110 isinflated or expanded as described above with respect to expandablemember 34, for example, by way of an inflation lumen extending throughguide wire 108. Tethers 112 may be provided on expandable member 110 toretract and manipulate it to within the interspinous space, asillustrated in FIG. 14C. Once expandable member 110 is properlypositioned within the interspinous space, distraction mechanism 100 maybe removed from the interspinous space immediately or, if the expandablemember has been filled with a curable expansion medium or one thatinvolves setting or hardening, the distraction mechanism may be kept inthe interspinous space until the desired consistency, curing orhardening has been achieved by the expansion medium. To removedistraction mechanism 100 from the interspinous space, its profile isreduced to a low profile state, as illustrated in FIG. 14D. As mentionedearlier, this is accomplished by translating proximal hub 104 aproximally along guide wire 108. Distraction member 100 may be retractedout through a cannula or removed directly in this low profile state,leaving expandable member 100 alone within the implant site asillustrated in FIG. 14E. Tethers 112 may then be cut or secured inplace. Optionally, a strap 116 or the like may be implanted to furthersecure expandable member 110 within the implant site and reduce the riskof migration. Here, bores or holes 114 have been formed through thethickness of the spinous processes 18, 22 and strap 116 threadedtherethrough with its ends secured together by a securing means 120,such as a suture, staple or clip, as illustrated in FIG. 14F.Alternatively, strap 116 could be wrapped around the spinous processes18, 22.

In addition to the expandable balloon spacers, the present inventionfurther provides for mechanically expandable spacers such as thoseillustrated in FIGS. 15-17. For example, expandable spacer 130 of FIG.15A is a cage-like structure having spaced-apart, parallel strut members132 extending between and fixed to hubs 134. Like the distractionmechanism of FIGS. 14A-14F, spacer 130 may be provided on anddeliverable by way of a guide wire 136 which is threadably engaged toand disengagable from proximal hub 134 a. After placement of spacer 130within the interspinous space, as illustrated in FIG. 15A, spacer 130 isexpanded by advancing proximal hub 134 a distally along guide wire 136thereby forcing struts 132 radially outward and away from each otherwhereby the expanded configuration of spacer 130 is elliptical or, in amore advanced state of expansion, substantially spherical. Once thedesired degree of distraction is achieved between vertebrae 2 and 4,guide wire 136 unthreaded from hub 134 a and removed from the implantregion.

FIGS. 16A and 16B illustrate another embodiment of an expandable spacer140 which is in the form of a coiled band 142 terminating at an outerend 144 having a configuration for receiving and locking onto inner end146 upon full expansion or unwinding of the coil. The diameter of coil142 in an unexpanded or fully wound state is small enough to allow easyinsertion between spinous processes 18, 22. Upon proper positioningwithin the interspinous space, coil 142 is allowed to expand and unwindthereby distracting vertebrae 2 and 4 apart from each other. Once thedesired level of distraction is achieved, inner end 146 is coupled toouter end 144. While the figures show band 142 inserted transversely tospinous processes 18, 22, it may alternatively be inserted in line or inthe same plan defined by the spinous processes.

FIGS. 17A-17C illustrate another interspinous spacer 150 havinginterlocked nested portions 152. Nested portions 152 are each shaped andconfigured to be received within one of its adjacent portions and toreceive the other of the adjacent portions when in a low profile state,as illustrated in FIG. 17A. Upon expansion of spacer 150, which may bespring loaded or be expandable by way of an instrument (not shown) whichmay be inserted into the spacer's center and rotated to flare portions152, vertebrae 2 and 4 are caused to distract from each other. Portions152 may have a configuration or shape which allow them to bite or diginto the spinous process 18, 22 and become securely retained therein.

FIGS. 18A and 18B illustrate another interspinous spacer 160 of thepresent invention in an undeployed or unexpanded state and a deployed orexpanded state, respectively. Spacer 160 includes an expandable tubularmember 162 having end portions 164 a, 164 b which are capped by hubs 166a, 166 b, respectively. As is explained in greater detail below, one orboth hubs may be provided fixed to tubular member 162 or may bereleasably coupled thereto. A sleeve or retaining member 168 iscircumferentially positioned about tubular between end portions 164 a,165 a. Most typically, retaining member 168 is positioned substantiallycentrally (as shown) on tubular member 162, but may be positionedlaterally towards one or the other end. Retaining member 168 has alength that covers about one third of the length of tubular member 162,but may be longer or shorter depending on the application. As isexplained in greater detail below, interspinous spacer 160 may furtherinclude a core member (shown in FIG. 21) within the lumen of the tubularmember and which may be provided integrated with spacer. Alternatively,the core member may be provided as a detachable component of the deviceused to deliver and implant the spacer (see FIGS. 19A and 19B).

In the undeployed state, as illustrated in FIG. 18A, spacer 160 has anelongated tubular or cylindrical shape, and may have any suitablecross-sectional shape, e.g., circular, oval, starred, etc., where themore angular cross-sections may allow the device to bite or dig into thespinous processes and for better retention. In this undeployed orlengthened state, tubular member 162 has a length in the range fromabout 20 mm to about 80 mm, and more typically from about 30 mm to about50 mm, and a diameter or average thickness in the range from about 4 mmto about 12 mm, and more typically from about 6 mm to about 9 mm. Assuch, spacer 160 is deliverable to an implant site between adjacentspinous processes in a minimally invasive manner.

In the deployed state, as illustrated in FIG. 18B, spacer 160 has adumbbell or H-shaped configuration, where the length of spacer 160 isless than and the diameter or height of spacer 160 is greater than thecorresponding dimensions of the spacer when in an undeployed state. Inparticular, the length dimension of the end portions 164 a, 164 b oftubular member 162 has been reduced by about 25% to about 70% while thediameter of the end portions 164 a, 164 b has been increased by about50% to about 600%, and the diameter of the central or sleeve-coveredportion has been increased by about 200% to about 400%, where thediameter of the portions of the tubular member 164 a, 164 b not coveredby retaining member 168 have a greater diameter than the portion oftubular member 162 which is covered by retaining member 168. Theincreased diameter of covered or central portion 168 distracts theadjacent vertebrae so as to provide pain relief. The diameter of hubs166 a, 166 b may remain constant upon deployment of device 160. In thisdeployed state, tubular member 162 has a length in the range from about15 mm to about 50 mm, and more typically from about 20 mm to about 40mm, and an end portion diameter in the range from about 10 mm to about60 mm, and more typically from about 15 mm to about 30 mm, and a centralportion diameter in the range from about 5 mm to about 30 mm, and moretypically from about 8 mm to about 15 mm. As such, when operativelyplaced and deployed within an interspinous space, the deployed spacer160 fits snugly within the interspinous space and is held in place bythe surrounding muscle, ligaments and tissue.

Any suitable materials may be used to provide a spacer 160 which isprovided in a first state or configuration, e.g., the undeployed stateillustrated in FIG. 18A, and which can be manipulated to achieve asecond state or configuration, and back again if so desired. Apolymer-based material or any other material which allows forsimultaneous axial shortening and radial expansion is suitable for useto form tubular member 162. The end portions 164 a, 164 b may be made ofthe same or a different material as that of the central or coveredportion. A flexible or shaped memory material or any other materialwhich also allows for simultaneous axial shortening and radialexpansion, but which is less expandable, i.e., maintains a compressiveforce about tubular member 162, than the material employed for tubularmember 162 may be used to form retaining member 168. As such, retainingmember 168 limits the extent of radial expansion as well as axialshortening that the covered portion of tubular member 162 can undergo.Examples of suitable materials for the retaining member include, but arenot limited to, Nitinol or polyethelene in a braided or mesh form.Further, the construct of retaining member 168 may be such that theradial force applied to the portion of tubular member 162 that it coversis constant or consistent along its length so as to maintain a constantdiameter along its length or, alternatively, may have a varying radialforce so as to allow for selective shaping of the covered portion oftubular member 162 when in a deployed state. Retaining member 168 may beconstructed so as to resist bending or flexing upon forcible contactwith the spinous processes and, as such, does not conform to the spinousprocesses. Conversely, the retaining member 168 may be constructed froma more flexible material that allows for some compression and, as such,may conform or be conformable to the spinous processes. Further, thephysical properties and dimensions of the materials used for both thetubular member and the retaining member may be selected to provide thedesired amount of distraction between target vertebrae.

Referring now to FIGS. 19A and 19B, spacer 160 is shown operativelyemployed within an interspinous space and coupled to delivery device170. Delivery device 170 includes an outer shaft 172 and an inner shaft178, movable relative (axially, rotationally or both) to outer shaft172, both extending from a handle mechanism 174. For example, innershaft 178 may be configured to be retracted proximally within outershaft 172, or outer shaft 172 may be configured to be advanced distallyover inner shaft 178, or both configurations may be employed together,i.e., while outer shaft 178 is advanced, inner shaft 178 is retracted.The relative movement may be accomplished in any suitable manner, forexample by way of a screw configuration, i.e., where the shaft membersengage by way of corresponding threads, as illustrated in FIG. 20A, orby way of a ratchet configuration, as illustrated in FIG. 20B. Therelative movement is accomplished by manual actuation of actuator 176coupled to handle 174. While only mechanical embodiments of the movementactuation are illustrated, the same can be achieved by electrically orpneumatically-driven devices or mechanisms.

As mentioned above, spacer 160 may be provided with an integrated coremember or the core member may be detachably provided on the distal end182 of inner shaft 178. In the first embodiment, distal end 182 of innershaft 178 is configured to temporarily couple with a proximal end (i.e.,the end closest to handle 174) of the core member. In the latterembodiment, the distal end 182 of inner shaft 178 is configured to beinserted into the lumen of tubular member 162, as illustrated in FIG.21, connected to or engaged with distal hub 166 b (i.e., the hubpositioned furthest from handle 174) and be detachable at a proximal end184 from inner shaft 178 to function as a core member. An advantage ofthe latter embodiment is that the end portion 182 of the inner shaft 178functioning as the core member may have a length that is as short as thelength of tubular member 172 when in a deployed state, with no extralength or remaining portion extending laterally of the implanted device.In the integrated embodiment, the core length may need to be as long astubular member 172 when in the undeployed state. However, the coremember may be segmented to allow for selective removal of one or morelengths or portions from the proximal side of the core member subsequentto implantation of the spacer so as not to have any excess lengthextending from the spacer.

With either embodiment, retraction of inner shaft 178, as describedabove, retracts distal hub 166 b toward proximal hub 166 a and/oradvancement of outer shaft 172 advances proximal hub 166 a towardsdistal hub 166 b, thereby causing tubular member 162 to be compressedaxially, and thus expanded radially, as shown in FIG. 19B. While distalhub 166 b may be fixed to tubular member 162, proximal hub 166 a may beprovided as a separate component having a central bore which allows itto receive and axially translate over inner shaft 178. Proximal hub 166a may be configured to readily slide over inner shaft 178 in a distaldirection (but possibly not in a proximal direction) or may be threadedin order to advance over inner shaft 178. The advancement of proximalhub 166 a axially compresses tubular member 172 and causes it toradially expand. The axial compression or radial expansion may becontinued until the desired extent of distraction occurs betweenvertebrae 2 and 4. When the desired level of distraction is achieved,proximal hub 166 a is secured to either the proximal end of tubularmember 162 and/or the proximal end of the core member 182, such as by athreaded or snap-fit engagement or by activating a lock mechanism (notshown). Inner shaft 178 may then be released from the core member (ordistal end 182 of inner shaft 178 may be released from inner shaft 178and left within tubular member 172 to function as the core member)which, along with the end hubs 166 a and 166 b, maintain the implantedspacer 160 in a deployed state so as to maintain distraction between thevertebrae.

The reconfiguration of spacer 160 may be further facilitated byselectively configuring the wall of tubular member 162. For example, theinterior or luminal surface of tubular member 162 may be contoured orincorporated with divets or spaces 180 where, upon compression oftubular member 162, the walls of the uncovered portions 164 a, 164 b oftubular member 162 will more readily fold inward to provide theresulting configuration shown in FIG. 18B.

The subject devices and systems may be provided in the form of a kitwhich includes at least one interspinous device of the presentinvention. A plurality of such devices may be provided where the deviceshave the same or varying sizes and shapes and are made of the same orvarying materials. The kits may further include instruments and toolsfor implanting the subject devices, including, but not limited to, acannula, a trocar, a scope, a device delivery/inflation/expansion lumen,a cutting instrument, a screw driver, etc., as well as a selection ofscrews or other devices for anchoring the spacer tabs to the spinousprocesses. The kits may also include a supply of the expandable bodyinflation and/or expansion medium. Instructions for implanting theinterspinous spacers and using the above-described instrumentation mayalso be provided with the kits.

The preceding merely illustrates the principles of the invention. Itwill be appreciated that those skilled in the art will be able to devisevarious arrangements which, although not explicitly described or shownherein, embody the principles of the invention and are included withinits spirit and scope. Furthermore, all examples and conditional languagerecited herein are principally intended to aid the reader inunderstanding the principles of the invention and the conceptscontributed by the inventors to furthering the art, and are to beconstrued as being without limitation to such specifically recitedexamples and conditions. Moreover, all statements herein recitingprinciples, aspects, and embodiments of the invention as well asspecific examples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents and equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure. The scope of the presentinvention, therefore, is not intended to be limited to the exemplaryembodiments shown and described herein. Rather, the scope and spirit ofpresent invention is embodied by the appended claims.

I claim:
 1. A method for stabilizing a subject's spine, the methodcomprising: delivering a spacer through a cannula and to a locationbetween a first protrusion of a first vertebra and a second protrusionof a second vertebra using a lateral approach; moving end portions ofthe spacer toward one another using a delivery device, which is coupledto the spacer and extends through the cannula; and separating thedelivery device from the spacer while the spacer is in an H-shapedconfiguration and a central section of the spacer is positioned betweenthe first and second protrusions.
 2. The method of claim 1, furthercomprising: after delivering the spacer through the cannula, radiallyexpanding the end portions and the central section to distract the firstand second protrusions, wherein the first and second protrusions arefirst and second spinous processes, respectively.
 3. The method of claim1, further comprising expanding the spacer until a superior U-shapedregion of the spacer holds the first protrusion and an inferior U-shapedregion of the spacer holds the second protrusion.
 4. The method of claim1, further comprising radially expanding the central section and the endportions.
 5. The method of claim 1, further comprising sliding one ofthe end portions along an elongate inner member of the spacer to causeexpansion of both end portions.
 6. The method of claim 1, furthercomprising causing relative movement between at least one of the endportions and a core member of the spacer to move the spacer from adelivery configuration toward the H-shaped configuration.
 7. The methodof claim 1, wherein the central section includes a retaining memberconfigured to distract the first and second protrusions.
 8. The methodof claim 1, further comprising moving the spacer from a deliveryconfiguration for delivery through the cannula to the H-shapedconfiguration, wherein the spacer in the delivery configuration has afirst maximum diameter and in the H-shaped configuration has a secondmaximum diameter, and wherein the first maximum diameter is less thanthe second maximum diameter.
 9. The method of claim 1, furthercomprising causing relative movement between an elongate member withinthe spacer and the central section to radially expand the end portions.10. The method of claim 1, wherein the delivery device controllablymoves the end portions of the spacer toward one another while the spaceris positioned directly between the first and second vertebrae, themethod further comprising expanding the spacer to gradually distract thefirst and second vertebrae contacting the central section of the spacerprior to separating the delivery device from the spacer.
 11. A methodfor stabilizing a subject's spine, the method comprising: delivering aspacer through a cannula positioned in the subject; delivering a centralsection of the spacer between a superior protrusion of a superiorvertebra and an inferior protrusion of an inferior vertebra; and afterdelivering the central section between the superior and inferiorprotrusions, translating a first end portion toward a second end portionof the spacer using a delivery instrument coupled to the spacer andextending through the cannula such that the superior and inferiorprotrusions are contained between the first and second end portions, andlocking the spacer in a deployed configuration while the central sectionis positioned to contact and hold apart the superior and inferiorprotrusions.
 12. The method of claim 11, further comprising: actuating asegmented core member, which extends through at least a portion of thecentral section, to move the spacer toward the deployed configuration;and after moving the spacer toward the deployed configuration,selectively adjusting a length of the segmented core member.
 13. Themethod of claim 11, further comprising: sequentially adjusting expansionof the spacer by moving a segmented core along the central section ofthe spacer, the segmented core is coupled to the delivery instrumentthat extends out of the subject.
 14. The method of claim 11, furthercomprising expanding the central section to distract the superior andinferior protrusions before locking the spacer.
 15. The method of claim11, wherein the first end portion has a bore through which a core memberextends, and wherein the core member is coupled to the second endportion.
 16. A method comprising: moving a spacer, in a deliveryconfiguration, through a cannula positioned in a subject; positioning acentral section of the spacer at a location between a superiorprotrusion of a superior vertebra and an inferior protrusion of aninferior vertebra, the spacer including a first end portion and a secondend portion; moving the first end portion toward the second end portionsuch that (a) the first end portion extends along a first side of thesuperior protrusion and a first side of the inferior protrusion and (b)the second end portion extends along a second side of the superiorprotrusion and a second side of the inferior protrusion, wherein thefirst end portion is moved toward the second end portion using adelivery instrument coupled to the spacer and extending through thecannula; and locking the spacer in an H-shape configuration.
 17. Themethod of claim 16, after positioning the central section between thesuperior and inferior protrusions, the method further comprising:expanding the first end portion; and expanding the second end portion.18. The method of claim 16, further comprising moving at least one ofthe first and second end portions through an interspinous space whilethe spacer is in the delivery configuration.
 19. The method of claim 16,wherein the first end portion is moved toward the second end portionuntil a superior U-shaped region of the spacer holds the superiorprotrusion and an inferior U-shaped region of the spacer holds theinferior protrusion.